MC9S08AC16_0911 Datasheet, PDF (295/336 Pages) Freescale Semiconductor, Inc – HCS08 Microcontrollers

Appendix A Electrical Characteristics and Timing Specifications
V_DD and multiply by the pin current for each I/O pin. Except in cases of unusually high pin current (heavy
loads), the difference between pin voltage and V_SS or V_DD will be very small.
Table A-3. Thermal Characteristics
Rating
Symbol
Value
Unit
Operating temperature range (packaged)
Thermal resistance ^1,2,3,4
T_A
T_L to T_H
°C
–40 to 125
48-pin QFN
1s
84
2s2p
27
44-pin LQFP
32-pin LQFP
1s
2s2p
θ_JA
1s
2s2p
73
56
°C/W
85
56
42-pin SDIP
1s
58
2s2p
47
1 _{Junction temperature is a function of die size, on-chip power dissipation, package thermal}
resistance, mounting site (board) temperature, ambient temperature, air flow, power
dissipation of other components on the board, and board thermal resistance.
2 _{Junction to Ambient Natural Convection}
3 _{1s - Single Layer Board, one signal layer}
4 _{2s2p - Four Layer Board, 2 signal and 2 power layers}
The average chip-junction temperature (T_J) in °C can be obtained from:
T_J = T_A + (P_D × θ_JA)
Eqn. A-1
where:
T_A = Ambient temperature, °C
θ_JA = Package thermal resistance, junction-to-ambient, °C/W
P_D = P_int + P_I/O
P_int = I_DD × V_DD, Watts — chip internal power
P_I/O = Power dissipation on input and output pins — user determined
For most applications, P_I/O << P_int and can be neglected. An approximate relationship between P_D and T_J
(if P_I/O is neglected) is:
P_D = K ÷ (T_J + 273°C)
Solving equations 1 and 2 for K gives:
Eqn. A-2
K = P_D × (T_A + 273°C) + θ_JA × (P_D)²
Eqn. A-3
where K is a constant pertaining to the particular part. K can be determined from equation 3 by measuring
P_D (at equilibrium) for a known T_A. Using this value of K, the values of P_D and T_J can be obtained by
solving equations 1 and 2 iteratively for any value of T_A.
MC9S08AC16 Series Data Sheet, Rev. 8
Freescale Semiconductor
295